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Old 18-02-2018, 12:48 PM   #21
Cudworth
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https://en.m.wikipedia.org/wiki/1N4148_signal_diode
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Old 19-02-2018, 12:56 PM   #22
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Quote:
Originally Posted by Tricky Dicky View Post
The two large ICs next to the relays are highly likely Darlington arrays and it is they that need protecting from the back e.m.f. not the switched outputs hence it is a certainty that the components identified earlier are the reverse diodes.
If those large ICs are ULN2803A's (which having 18 pins seems likely), they have diodes built in for just this purpose, commoned to pin 10. If so, pin 10 of each IC should be seen to connect to the positive relay supply terminal.
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Old 07-03-2018, 09:23 AM   #23
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I have been following this thread and as I am about to build some relay boards for point motors, am I right that the reverse diode goes across the relay coil not the contacts. My relays are operated via a non locking push switch at 12V with 24V from a CDU through the contacts.
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Old 07-03-2018, 03:33 PM   #24
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Across relay coils are where Bemf diodes are a benefit.
The other place is the coils of solenoid motors, again used to remove Bemf when power is disconnected from the coil. However, this is often overlooked by many solenoid point motor users!
Don't forget though they have to be fitted the right way around!
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Old 08-03-2018, 08:03 AM   #25
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Thanks for that.
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